Associate Professor Peter Tuthill, research astrophysicist at the University of Sydney, says although very thin galaxies are common, photographs like this one are rare.

"It's no more than just a freaky chance to see it in this alignment; but that of itself doesn't tell you anything amazing about the physics," Associate Professor Tuthill said.

Bad Astronomy blogger Phil Plait says the chances of photographing a galaxy like this is similar to flinging a handful of loose change into the air and taking a flash photograph. If you fling enough coins up, eventually one of them will be snapped edge-on.

William Herschel first trained his telescope on NGC 4452 in 1784. He described the object as a bright nebula, small and very much elongated.

NGC 4452, a 35,000-light-year-wide galaxy in the Virgo cluster, is unusual because of its almost uniform thickness.

Spiral galaxies like the Milky Way usually bulge noticeably at the centre.

NGC4452 maintains a width-to-thickness ratio of about 100:1 compared to the Milky Way's 40:1 ratio.

Our side-on view of NGC4452 makes it difficult to tell what kind of galaxy it really is. NASA speculates that a view from above would reveal a classic spiral structure.

Pure guesswork

"It's a mystery," Associate Professor Tuthill says, "because you're only seeing it from side on and you don't really know what it looks like. But if it's a spiral you would think that it should have a bigger bulge."

The fact it doesn't show the usual clouds of dark dust indicates that it might be a low-dust lenticular galaxy, NASA says, but it's also possible that infrared filtering has hidden a dust lane.

"Normally when you see these things side on you see these dramatic dust lanes; there's this gunk in the galactic plane which blocks out some of the light from the stars," Associate Professor Tuthill said.

He says working out the structure of a galaxy always involves a bit of guesswork.

"If you actually knew what it looked like from the top at the same time, that would give you quite a powerful data set because it is hard to unravel both pieces of the puzzle for any galaxy.

"That's the problem we're confronted with in our own galaxy in a way. All we see of our own galaxy is this thin band of light.

"It's a fairly new finding that the Milky Way is a galaxy called a barred spiral, not a simple spiral.

"Nobody really knows how many arms there are in our galaxy. It's kind of this problem that we can't see the forest because we're in amongst the trees. I guess that is well-illustrated by this particular galaxy."

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